Field of the Invention
The present invention relates to a method and apparatus for cleaning and inspecting the bottom surfaces of fluid reservoirs, such as storage tanks, pools, sumps, and ponds, without first draining them. More particularly, the invention relates to a remote controlled, submersible vehicle which removes sediment from reservoir surfaces by a scrubbing and/or vacuuming process and simultaneously provides video and/or acoustic inspection of the freshly cleaned surface.
In recent years, environmental and industrial safety concerns have focussed attention on the need to inspect fluid handling facilities for signs of corrosion and structural defects. The use of fluid reservoirs to store fuels, chemicals, waste, and radioactive effluents is common in many industries, particularly the chemical and nuclear power industries. In addition, some fluid reservoirs are involved in the active processing of liquids. These reservoirs are subject to additional stresses since liquids often move through them at elevated temperatures and high velocities. When used for either purpose, the volume and nature of the liquids involved make these reservoirs potential sources of widespread toxic and radioactive contamination. As a result, monitoring their structural integrity is a primary concern of government and industry alike. The consequences of failing to detect structural by the media and in court proceedings before the regulatory agencies.
Inspection of liquid reservoirs is no simple matter since entire systems often must be shutdown to gain access to them. Even where the reservoir is not a part of an active processing system, inspection is impeded by the stored liquid and the inevitable buildup of sediments on the reservoir surfaces. In addition, the suspension of sediment in the fluid itself impedes inspection since these particles reduce visibility and scatter signals which may be used to remotely examine the surfaces. Thus, suspended particles will significantly reduce the resolution of video or acoustic images, limiting the features that can be detected.
The most obvious solution to the difficulties imposed by suspended particles and sediment buildup is to drain and clean the reservoir prior to inspection. However, there are significant problems with this approach. First, operation time is lost as systems which depend upon the reservoir are shut down during the cleaning and inspecting procedure. Second, manpower is tied up by these procedures. Finally, where toxic chemicals or radioactive waste are implicated, personnel are exposed to dangerous conditions. For example, in the nuclear power industry radioactive sediment collects in water filled cooling pools. This water provides shielding against radiation and prevents the escape of radioactive particles. Draining these pools to clean and examine their surfaces removes this shielding, exposing personnel to high radiation levels. In addition, if the sediment dries it is susceptible to wind borne dispersion, increasing the dangers to other on-site personnel and the surrounding communities.
Remote controlled, submersible vehicles have been used in various industries to remove sediment from undrained storage tanks. While the use of these vehicles addresses the dangers and economic costs associated with draining reservoirs for cleaning, the contemporaneous inspection of the reservoir surface for damage or defects is not known to have been practiced. As discussed in connection with the description of the present invention, cleaning and inspection procedures are interrelated and it is more efficient to deal with them concurrently.
Sedimentation is a continuous process, proceeding even as the deposited materials are removed. Thus, fresh sediment will accumulate in the interval between cleaning the surface and inspecting it. Minimizing this interval is one key to obtaining accurate inspection data. On the other hand, the contemporaneous cleaning and inspection of surfaces creates a new problem since scrubbing a surface agitates deposited sediment, thereby increasing the concentration of sediment particles suspended in the liquid. As a result, the scattering problem described earlier may be exacerbated when surface cleaning and inspection are carried out in a one step process.
In addition to the problems created by solid sediments, the suspension of non-miscible liquids creates difficulties in certain storage environments. For example, where oil-based liquids are stored, accumulated moisture may also be present, suspended in the liquid. The consequent inhomogeneity of the liquid leads to the same signal scattering and resolution problems discussed above. The quality and resolution of the images necessary to accurately inspect liquid reservoirs is determined by the size of the features which indicate the presence of structural defects and corrosion. Unfortunately, these features may be as fine as hairline cracks, which are easily obscured by small amounts of sediment or missed in low resolution images. Thus, any image degradation could hinder the timely discovery of structural defects and result in contamination with toxic or radioactive material. Certain features, such as corrosion on the external surface of tanks, grain boundary corrosion, or subtle wear effects, cannot be detected visually under the best of circumstances. In these instances, ultrasonic inspection methods are necessary. Ultrasonic inspection can detect variations in reservoir wall thickness due to corrosion on either the inside or outside wall surface as well as structural defects within the reservoir walls. However, ultrasonic inspection requires the detection of small changes between incident and reflected signals. Consequently, the technique is equally sensitive to the accumulation of sediments on reservoir surfaces and the scattering of signals by suspended particles.
Accordingly, it is a primary object of the present invention to facilitate the cleaning and inspection of a reservoir surface without draining the reservoir of its contents.
It is also an object of the present invention to remove sediment from a reservoir bottom by breaking it up mechanically and vacuuming it away.
It is a further object of the present invention to filter the suspension of sediment and reservoir fluid and return the filtered fluid to the reservoir.
Yet another object of this invention is to minimize the time between surface cleaning and surface inspection, during which sediment can continue to deposit.
A further object of the present invention is to provide a liquid volume free of suspended particles through which optical and ultrasonic inspection signals can pass unscattered.